On the fixed-income side of your investment portfolio, something like the Vanguard Total Bond Market ETF (BND) and Vanguard Total International Bond ETF (BNDX) provide exposure to diversified U.S. and international debt. BND has a 0.08% expense ratio and BNDX has a 0.20% expense ratio. [Craft An Investment Portfolio Using 5 ETFs]

If an investor wants to customize his or her exposure, there are plenty of options as well.

For example, investors can break down asset class categories into large-, mid- and small-cap, with the Schwab U.S. Large-Cap ETF (SCHX) , which has a 0.04% expense ratio, iShares Russell Mid-cap ETF (IWR) , which has a 0.22% expense ratio and Vanguard Small Cap ETF (VB) , which has a 0.09% expense ratio.

Investors can also target specific sectors. The energy sector has been outperforming this year, and investors can capture the growth through a sector ETF like the Vanguard Energy ETF (VDE) . VDE is up 13.7% year-to-date.

There are also options that income-minded investors may find attractive. Those who are seeking income generation can look at high-yield options in both stock and bond ETFs. The Vanguard REIT ETF (VNQ) , which holds real estate investment trusts, has a 2.7% 12-month yield. Bond investors can browse through speculative grade debt funds, like the SPDR Barclays High Yield Bond ETF (JNK) , which has a 4.6% 30-day SEC yield, and the actively managed AdvisorShares Peritus High Yield ETF (HYLD) , which shows a 7.74% 30-day SEC yield. In addition, iShares U.S. Preferred Stock ETF (PFF) , which act like a type of hybrid security, shows an attractive 6.5% 12-month yield.

As always, investors should do some due diligence of their own before jumping into any investment. There may be a number of ETFs that cover a similar market segment, so investors will have to dive deeper and understand how the varying products differ from one another.

The opinions and forecasts expressed herein are solely those of Tom Lydon, and may not actually come to pass. Information on this site should not be used or construed as an offer to sell, a solicitation of an offer to buy, or a recommendation for any product.